Policy based data migration in a hierarchical data storage system

Abstract

A hierarchical data storage system including a policy based migration engine to select a migration policy and migrate data from a first set of removable storage media, such as tape cartridges, to a second set of removable storage media in accordance with the migration policy. The hierarchical data storage system further includes a control unit including a processor, a host interface to couple the processor to a host, a library manager interface to couple the processor to an automated tape library, a storage device interface to couple said processor to a storage device, and a memory unit.

Description

BACKGROUND [0001] 1. Technical Field [0002] The present invention relates generally to data storage and data processing. More specifically, the present invention relates to efficient data management within a hierarchical data storage system. [0003] 2. Description of the Related Art [0004] In a hierarchical data storage system, fast-access storage devices are combined with arrays of relatively slower, less frequently accessed storage devices. As an example, frequently accessed data is generally stored on relatively expensive fast-access storage devices such as direct-access storage devices (DASD), while less frequently accessed data is generally stored on relatively less expensive, slower storage devices such as sequential-access storage media (e.g., tape media). The combination of storage devices in this way helps balance the costs of storing data with the speed at which the data must be accessed. [0005] An example of a hierarchical storage system is a virtual tape storage system (V...

AI Technical Summary

Benefits of technology

[0014] It has been discovered that by grouping tape cartridges into logical groups called pools, defining reclamation policies, and associating one or more of the reclamation policies with a particular pool, a process can be used to efficiently migrate data from one or more source cartridges to one or more destination cartridges, greatly improving the data management of a hierarchical storage system, such as a Virtual Tape Server (“VTS”). As used herein, migrating data can constitute copying data from a source to a destination if one or more conditions are satisfied. The present invention thus provides more storage space within the VTS, decreased cost associated with the management of the VTS and storage of data within the VTS, and improved efficiency in transferring data from one set of tape cartridges to another set of tape cartridges.

Problems solved by technology

As an example, frequently accessed data is generally stored on relatively expensive fast-access storage devices such as direct-access storage devices (DASD), while less frequently accessed data is generally stored on relatively less expensive, slower storage devices such as sequential-access storage media (e.g., tape media).

The space consumed by the inactive data, however, is unusable and cannot be overwritten (this is because of the characteristics of tape media, once a tape is full of data, no additional data may be written to the tape).

While known techniques of reclamation are available to manage storage efficiency, limitations exist.

One limitation with respect to reclamation is that the implementation of reclamation is dependent upon the percentage of active data on a source cartridge falling below a predefined threshold.

This presents an efficiency problem in that not all data is expired by a host at the same rate or using the same criteria.

This may result in a particular cartridge never falling below the specified threshold, yet have a relatively high percentage of inactive data.

Since a VTS can contain thousands of tape cartridges, the percent of wasted space in a VTS can be significant.

Because of the amount of storage accessible within a VTS, as well as the different formats of storage, the efficient management of data and storage resources of a VTS is very challenging, even with the aid of pooling and reclamation.

In addition to the limitations above, common difficulties associated with managing data in a VTS include efficient management of storage space on individual cartridges as well as accommodating for different cartridge formats within the VTS.

A difficulty arises if a user of the VTS wishes to consolidate all tape drives of VTS to a single tape drive format or to different formats.

By consolidating to a single format, and / or switching to different formats, the user runs the risk of having a number of obsolete tape cartridges (e.g., not compatible with the new drive format).

As a result, the data on the cartridges will be inaccessible, unless the data can be migrated to media compatible with the drives in the system.

Unfortunately, there is no known way to efficiently migrate such data.

A similar problem results for a user that desires to upgrade to a new drive format, which may require the use of new cartridges and migration of active data contained on incompatible cartridges.

These challenges and others are made more difficult for VTS systems which include thousands of tape cartridges.

Unfortunately, known methods of migration require a user to identify, cartridge by cartridge, the source data to be migrated.

This can be a time consuming, and often error-prone process.

The down-time and errors may translate into real economic loss for a business relying on the accessibility and accuracy of the data.

Additionally, known migration methods are limited in their ability to efficiently transfer data to one or more destination cartridges.

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